Folliculogenesis

What are the parts of the follicle?

~oocyte: oogenesis, development of the oocyte

~granulosa cells: inside, receive T from theca and make E2

~thecal cells: outside, produce T

~follicular fluid: main system for communication

Components of oocyte

~zona pellucida: assists fertilization and may provide protection, thick, hardened shell, protects

~Vitelline membrane: surface layer of the oocyte, perivitelline membrane

~Cytoplasm (yolk)- contains many proteins, enzymes, nutrients needed for survival of the zygote

~Germinal vesicle- nucleus containing genetic information

Oogenesis

~oogenesis: formation and development of the ovum (egg), primordial gonadal ridge, tunica albicania, why we have set # of cells

~oogonium: primordial cell which develops into the oocyte, earliest stage

~oocyte: early, not yet fully developed ovum

~ovum (the egg): the cell that is capable of developing into a new individual

Oocyte formation & Atresia

~primary oocytes form from mitosis of oogonia

~primary oocyes enter MEIOSIS I, become dormant

~max number formed during mid to late fetal life

~once max number is attained, atresia (natural degeneration begins and continues for life/loss of germ cells)

Oocyte activation & development PART 1

~primary oocytes are surrounded by follicle cells in primordial follicles: remain inactive

~follicles develops from primordial to primary: increase in size of the primary oocyte, fluid and add layers there to protect them

~MEIOSIS NOT YET REACTIVATED

Compare follicles and oocytes

Follicles: pri → 1 → 2 → 3→ pre ov

oocyte: 1 → 1 → 1 → 1 THEN LH surge → 2 oocyte (polar body) → final stage ovum (haploid) or 2 Pb still

Oocyte activation & development PART 2

~meiosis resumes only in preovulatory follicle(s): LH and FSH remove inhibitors

~activation occurs at estrus, lose control continues to MEIOSIS II

~ONLY a selected few are stimulated to develop, very few see LH surge

~repeats every cycle

What is the overall trend of oocyte number as females age?

~they reduce as you get older and once menopause hits we don’t have any left

In cattle, what is the oocyte number trend? Other facts?

~fetal: 2,700,000

~birth: 70, 000

~puberty: 24,000

~number ovulated in a lifetime? human: ~500, cow: ~350

What happens to the oocyte versus the cells around it as they mature and prepare for fertilization?

~the oocyte stays in M1 while the surrounding cells are what change

~so when the fertilization occurs, the inhibition created by the surrounding cumulus granulosa cells gets removed and since the cells are not as tightly packed around the oocyte, it goes from primary to secondary

Primordial follicle

~single layer of squamous epithelial cells

~resting state

~cues to grow? growth factors like (anti-Mullerian) after puberty

Primary follicle

~single layer follicle cells

~primary oocyte but starts to expand

~follicle cells expand (cubodial)

~zona pellucida forms: hardened layer on outside

~OOCYTE FROZEN IN MEIOSIS I

Secondary follicle

~primary oocyte

~multiple layers of granulosa cells

~thecal layer forms

~pre-antral: no follicular fluid

~start to see a division

~still in a primary oocyte frozen in MEIOSIS I

Folliculogenesis

~classification and regulation of follicle growth

~growth and development of follicles, tertiary follicle

~parts of follicle: granulosa and thecal cells, follicular fluid

~follicular fluid: reservoir for nutrients, communication, growth factors, and hormones

~still frozen in MEIOSIS I

What part of the granulosa cells provide E2 and what part produces the inhibition? What allows the cells to produce E2?

~The mural produce the E2 and the cumulus produce the inhibition

~T from thecal goes into mural then makes E2

Granulosa and Theca: 2 cell 2: gonadotropin model

~granulosa: cortex, responsive to FSH. convert T to estradiol

~theca: from stroma, responsive to LH, convert cholesterol to testosterone

~LH go to receptor on theca membrane, starts cholesterol, to preg to prog to create T for itself

~some go into mural where FSH goes to the receptor to activate aromatase to change T to E2

Follicular fluid (antral follicles)

~components:

1. hormones: steroids, gonadotropins, prostaglandins

2. proteins

3. enzymes

4. carbohydrates

~functions:

1. supports follicle growth

2. aids in oocyte development & health

3. mediates granulosa cell functions

~follicular: help keep it alive, live in hypoxy environment

Stages of follicular development

1. recruitment: increase # follicles: atresia (death) and E2 in small amount

2. selection (refinement): decrease # follicles, increase the size of follicle, increase E2 more, atresia

3. dominance: only one follicle, reaches max size, E2 in TREMENDOUS AMOUNTS, atresia

Early antral (tertiary)

~primary oocyte

~oocyte reaches maximum size

~granulosa cells exapnd

~antrum forms

~thecal layer more prominent: interna and externa= T

Graafian follicle (pre ov)

~last stage of the tertiary follicle

~primary oocyte

~max amount of cells and fluid

~largest dominant follicle

~cumulus-oocyte complex expelled at ovulation

Follicular development

~how do they grow?: waves and numbers

~stimulated or regulated by? gonadotropins: FSH and LH, growth factors, activin or inhibition

~activin: small,membrane inhibition: cumulus cells, regulate FSH/ what is present on the follicle

~fates: ovulation, atresia, cysts

Facts about Cysts

~PCOS, small recruiting follicles

~disease situations cause

~cystic ovaries (anything greater then 25cm), high-producing dairy cows,

~don’t die, don’t regulate

~lower P4, E2

~ALL has to do with metabolism

PCOS facts

~ a common hormonal disorder that affects 5 to 10% of women

~ continuous exposure to estrogen: blocks the LH surge, increases the thickness of the uterine endometrium

~strong association with obesity

~various treatments available depending on the severity of the condition

Follicle growth

~many recruited, few selected, one dominant follicle

~litter-bearing do codominant

~one does monovulatory

Waves of follicular growth

~ovulatory v.s non-ovulatory

~dominant vs. subordinate

~signals: LH, FSH, inhibition (dominant follicle)

First wave…

~ non-ovulatory wave: goes away more room

~recruitment, selected, dominant, atretic from each phase, and then atretic overall

~occurs after ovulation because progesterone is high

Second wave…

~non-ovulatory wave

~GNRH, FSH, LH

~same as first wave with R, S, D, Atresia

What are the two main signal hormones for follicle growth?

~FSH and LH

Follicle growth: FSH

~Granulosa cell mitosis: increase from increase E2, need T too

~increases LH receptors: more sensitive to LH

~Steroidogenesis: increase E2

~effects prenatal & antral follicles

Luteinizing Hormone

~Cholesterol: testosterone

~steroidogenesis

~effect antral follicles

~surge starts ovulation

~resumption of meiosis- oocyte (frozen in I until LH surge)

Ovulatory wave

~same as other waves but due to luteolysis of CL, the dominant follicle develops and ovulation occurs

~cows are more fertile when they have 2 to 3 waves but can be fertile 1 to 6

What happens because of the presence of the dominant follicle?

~inadequate production of gonadotropins

~steroids: estrogen and androgens

~inhibition: protein produced by follicles that inhibits other follicles from developing by decreasing FSH release: FSH is critical for the subordinate. The dominant follicle inhibits it

~negative impact on the subordinate, takes up a lot of space

Follicular growth

~growth, plateau, regress? P4, ovulate? decrease P4

Hormonal regulation

1. First GnRH from the hypothalamus ( stimulates GnRH)

2. FSH, LH stimulates growing follicle

3. slightly elevated estrogen level, (inhibits hypo)

4. high estrogen level (stimulates, Hypo)

5. LH, FSH, surge (stimulates ovulation and CL)

6. Ovulation

7. Corpus Luteum

8. estrogen and progesterone (inhibits, hypo)

Relation of LH, FSH, E2 on follicles in follicular growth

~recruitment: small follicles, small E2, LARGE FSH, low LH (still needed for T for E2)

~selection: medium follicles, increased E2, fewer selected follicles, lower FSH (presence of inhibition, granulosa cells), increased LH

~Dominance: SURGE E2, inhibition increased more, really low FSH, high LH

Question: What would you do if you were a producer and you wanted to increase the number of ova produced by your prize?

~Increased # go to recruitment

~give lots of FSH, more ova, prevent atresia

~superovulation protocol

Ovulation

~Stimuli: LH surge, FSH: don’t really know why its there

~Specific cascade of events

1. degradation of the follicle wall

2. extrusion of oocyte: resumption of meiosis

3. collapse of the follicle

Preovulatory follicle: Increase pressure

~increase PGE2 (vasodilator, increase edema)

~increase PGF2a (increase contraction of ovarian muscle)

Preovulatory follicle: Follicle wall weakens

~increase PGF2a: release of lysosomal enzymes, theca + Gran, chew away follicular wall

~shift from E2 to P4 by dominant follicle, increase P4 and then increase Collagenase

~increase Collagenase: breaks extracellular matrix, weakens the follicular wall